As is well known, during the initial and recovery stages of surge in turbocompressors, changes in load are very fast, resulting in increased vibration, thrust, temperature, and speed. The rapid excursion of these variables beyond their safe limits can cause extensive damage in only a few seconds. These same dangerous excursions can be experienced as a consequence of load rejection which is attributed to sudden large changes in load.
Rapid flow reversals during surge result in a rapidly changing load. In turn, the rate-of-change of fuel to the combustor of the gas generator turbine can be extremely high. In attempting to compensate for an increase in speed of the power turbine during the initial stage of surge, the fuel control system will begin closing the fuel valve. Inversely, in the recovery stage of surge, when turbocompressor speed falls, the fuel control system commences opening the fuel valve. It is during this recovery stage, when attempting to compensate for reduction in speed, that a rapid increase of fuel to the combustor may lead to dangerous excursions in temperature, causing high temperatures in gas turbine elements. Previously available fuel control methods failed to account for these turbine parameter excursions, and as far as known, there is no background art relative to this subject matter.
For the foregoing reasons, there is a need to easily and accurately prevent the onset of dangerous excursions of the parameters of gas turbines driving turbocompressors. A method that overcomes prior drawbacks would be to rapidly reduce the fuel valve setting at the onset of surge, or at the detection of load rejection, then limit the rate at which the fuel control system's output is allowed to relocate the fuel valve during the recovery stage. Then (after recovery) gradually return the allowable rate to the level of normal operation.